﻿// Copyright 2016 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef CC_BASE_SPIRAL_ITERATOR_H_
#define CC_BASE_SPIRAL_ITERATOR_H_

#include "base/logging.h"
#include "cc/base/cc_export.h"
#include "cc/base/index_rect.h"

namespace cc {

// The spiral iterator which iterates based on directions around the center
// rect in the given region. If the center rect is at index (2, 2), spiral
// iterator gives following sequence on iterating.
//
//    x 0   1   2   3   4
//  y ┌───┬───┬───┬───┬───┐
//  0 │ 16│ 15│ 14│ 13│ 12│
//    ├───┼───┼───┼───┼───┤
//  1 │ 17│  4│  3│  2│ 11│
//    ├───┼───┼───┼───┼───┤
//  2 │ 18│  5│  *│  1│ 10│
//    ├───┼───┼───┼───┼───┤
//  3 │ 19│  6│  7│  8│  9│
//    ├───┼───┼───┼───┼───┤
//  4 │ 20│ 21│ 22│ 23│ 24│
//    └───┴───┴───┴───┴───┘
class CC_EXPORT SpiralIterator {
public:
    SpiralIterator();
    SpiralIterator(const IndexRect& around_index_rect,
        const IndexRect& consider_index_rect,
        const IndexRect& ignore_index_rect);

    ~SpiralIterator() = default;

    operator bool() const;
    SpiralIterator& operator++();
    int index_x() const { return index_x_; }
    int index_y() const { return index_y_; }

private:
    int current_step_count() const
    {
        return (direction_ == UP || direction_ == DOWN) ? vertical_step_count_
                                                        : horizontal_step_count_;
    }

    bool needs_direction_switch() const;
    void switch_direction();

    enum Direction { UP,
        LEFT,
        DOWN,
        RIGHT };

    IndexRect around_index_rect_;
    IndexRect consider_index_rect_;
    IndexRect ignore_index_rect_;
    int index_x_;
    int index_y_;

    Direction direction_;
    int delta_x_;
    int delta_y_;
    int current_step_;
    int horizontal_step_count_;
    int vertical_step_count_;
};

} // namespace cc

#endif // CC_BASE_SPIRAL_ITERATOR_H_
